Field of the Invention
Sodium chloride and calcium chloride are the most common road deicing salts in use today. Sodium chloride is somewhat less expensive due to its high deicing efficiency and the wide distribution of natural deposits throughout the United States. Sodium chloride occurs naturally in a substantially pure state and hence needs only to be mined and ground to the appropriate particle size for storage, shipment and use.
On the other hand, calcium chloride is widely used as a road deicer and also as a antidusting agent for roads in the summertime. Calcium chloride is produced in large quantities as a co-product of the Solvay process for manufacturing soda ash.
Because sodium chloride and calcium chloride are nominally the least expensive road deicing salts, they are the most widely used road deicers in the United States. Annual use of sodium chloride for road deicing in the U.S. exceeds 9,000,000 tons.
Unfortunately, it has recently come to light through environmental studies that the costs of buying and applying sodium chloride and calcium chloride road deicers are misleading indices of the total cost of using these deicers. It has been estimated that damage to vehicles and highway structures through corrosion, and damage to flora, fauna and water supplies inflates the true cost to 14-22 times the nominal cost of manufacturing sodium chloride salt.
Various federal agencies in recent years have been advocating the replacement of calcium chloride and sodium chloride as road-treating agents. To date, there are no known cheap and environmentally acceptable alternative deicers to sodium chloride or calcium chloride.
Sodium is considered an environmental pollutant and chloride ions greatly contribute to the corrosion of metallic surfaces. In rural areas a higher proportion of chlorine in a road deicing agent may be tolerated, whereas in urban or suburban areas a lower proportion of chlorine in deicing agents is desired. Thus, there has been a need in the art for a deicing agent having a versatile and variable chlorine content for use in different environmental areas.
One end result of the efforts to find a cheap and environmentally safe road deicer culminated in a report by Bjorksten Research Laboratories which developed a salt known as calcium magnesium acetate as a substitute for sodium chloride. Unfortunately, the Bjorksten calcium magnesium acetate salts showed a tendency to attack portland cement concrete, possibly due to the acid content of those salts. The problem of calcium acetate and calcium magnesium acetate containing undissociated acetic acid was addressed in my copending application Ser. No. 316,816.
A major obstacle in the use of pure calcium acetate road deicing salt is its high cost of manufacture. This high cost of manufacture is due to the high cost of the raw material acetic acid needed to produce calcium acetate. Until an inexpensive source of acetic acid is developed, the prospects for commercial development of calcium acetate, as a road deicing agent, are not promising. Thus, there has been a further need in the art for a method of producing and using calcium acetate road deicing salts which makes calcium acetate economically viable as a substitute for either calcium chloride or sodium chloride.
Furthermore, both technical grade calcium chloride and commercial grade calcium chloride (CaCl.sub.2.2H.sub.2 O) are deliquescent. This can pose serious problems in the shipping and handling of the solid crystals, making it necessary to isolate the crystals from water in the atmosphere. Thus, it is another important object of the present invention to provide a road deicing agent which is non-deliquescent and hence does not present these difficult handling, shipping and storage problems.
It is also an important object of the present invention to provide an environmentally safe, yet commercially priced road deicing salt as a substitute for either sodium chloride or calcium chloride.
It is another important object of the present invention to provide a liquid freezing-point depressing agent having good handling, shipping and storage properties and which is environmentally safe.